1. Field of the Invention
The present invention relates to an automatic frequency monitoring circuit, an electronic device, an automatic frequency monitoring method, and an automatic frequency monitoring program that monitor a frequency of a clock related to an operation of a device to be monitored.
2. Description of the Related Art
Recently, electronic devices operate based on various clocks depending upon a type of a device. The monitoring of a clock has become more important as a reliability, availability, serviceability (RAS) function that maintains reliability, availability, and serviceability of operations of the electronic device.
For example, in Japanese Patent Application Laid-open No. H4-306930, a clock abnormality detector is disclosed that determines whether a frequency of a monitoring target clock is within a predetermined range. Because of the clock abnormality detector, the clock abnormality can be detected in an early stage.
Further, in Japanese Patent Application Laid-open No. H4-233349, to detect a frequency abnormality of an internal clock for master-slave synchronization with an external clock, an external clock abnormality detecting circuit is disclosed that notices the abnormality when the number of detections of a phase difference between the external clock and the internal clock is equal to or more than a predetermined value.
However, in the conventional technologies that are represented by Japanese Patent Application Laid-open Nos. H4-306930 and H4-233349, when the frequency of the clock is increased to improve the performance of the electronic device when the monitoring target clock is provided externally, a configuration of the device itself is not required to be changed but the configuration for detecting the clock abnormality is required to be changed.
Further, because a threshold that determines the abnormality of the clock is already fixed, even when the threshold is to be changed after the clock monitoring is started, the configuration for detecting the clock abnormality is required to be changed.